Various chemicals are being administered to various species of non-human primates to obtain comparative data on the response of non-human primates and rodents to known carcinogens and to materials suspected to be carcinogenic for humans. In addition, it is hoped that biological markers which will aid in the diagnosis of preneoplastic change as well as for frank neoplasia will be developed. Thus far seven chemicals have induced tumors in Old World monkeys; these are diethylnitrosamine, dipropylnitrosamine, 1-nitrosopiperidine, methylnitrosourea, methylazoxymethanol acetate, aflatoxin B1 and procarbazine. The serum levels of alpha-fetoprotein by radioimmunoassay in monkeys with biopsy-proven liver tumor were scattered over a wide range of 100,000 fold variation which is analogous to the range seen in human hepatocellular carcinoma. Studies have been undertaken to try to prevent hepatic carcinogenesis in non-human primates by pretreatment with various nucleophiles such as cysteamine and cysteine before administration of the carcinogen. BIBLIOGRAPHIC REFERENCES: Adamson, R. H., Correa, P., Sieber, S. M., McIntire, K. R. and Dalgard, D. W.: Carcinogenicity of aflatoxin B1 in rhesus monkeys: two additional cases of primary liver tumor. J. Natl. Cancer Inst. 57: 67-73, 1976. Waldman, T., McIntire, K. R., Dalgard, D. W. and Adamson, R. H.: The metabolism of tumor related proteins. In Bianchi, R., Mariani, G., and McFarlane, A. S. (Eds.): Plasma Protein Turnover. Baltimore, Md., University Park Press, 1976, pp. 155-164.